The SVS SB13-Ultra powered subwoofer features a 13.5" driver with 50mm peak excursion. It is driven by a 1,000 watt RMS Class D amplifier (3,600 watts peak). This amp has a dual band parametric equalizer and a unique limiter circuit that retains dynamic shadings even when pushed hard. The sub is a sealed box design with tight and clean bass. In fact, my nearfield THD+N (1 foot) measurements were all under 0.33% from 28 - 100Hz at 100dB!